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An Environmentally Friendly Mosquito Repellent?

By Cornelia Dean August 26, 2009 1:24 pmAugust 26, 2009 1:24 pm

A report this week in the journal Nature is taking me back to my childhood summers in New Jersey, where evenings were often marked by the appearance of a slow-moving Jeep towing a battered cart. A machine, about the size of a lawn mower, sat on the cart, spewing a whitish mist — DDT.

The town did the spraying in recognition of the fact that New Jersey was the mosquito core of the universe, a place, it was said, where an only-average sized insect could bring down a deer. Some of us called the mosquito the state bird.

My friends and I would dash along behind the jeep, running in and out of the gassy cloud, breathing in the strong odor of the insecticide as droplets condensed on our clothes and skin. As far as I know, this experience left no ill effects, except a persistent skepticism about claims that exposure to this, that or the other chemical is inevitably a health disaster.

Still, I accept the idea that widespread use of DDT caused environmental problems. The chemical persists in the flesh of animals that come into contact with it, and it concentrates in creatures at the top of the food web, like the fish-hunting ospreys I see often when I am at the coast. Because DDT can thin the shells of their eggs to the cracking point, widespread use of the chemical almost led ospreys and other raptors to extinction. When I see ospreys now I am reminded of how good it is that little jeep and its cart are long retired.

Unless, of course, the bugs are biting. Then, if it were up to me, I would crank up the sprayer and let loose a chemical blast. And for me mosquitoes are just an annoyance. In many parts of the world they are a deadly menace, spreading diseases like malaria.

That’s where the Nature paper comes in.

It is a description of work led by Anandasankar Ray, an entomologist at the University of California, Riverside, on fruit flies and their sensitivity to carbon dioxide. The researchers report that they have identified a compound that blocks the ability of the insects to detect it.

Clouds Hill ImagingCulex mosquitoes are vectors for many diseases.

The finding is interesting because it is the carbon dioxide we exhale that draws mosquitoes to us. A chemical that blocked that attraction would, in a sense, make us invisible to the insects. That is what seems to have happened when the researchers tested it on a class of mosquitoes — the genus Culex, which spreads West Nile Disease and other ailments.

It is too soon to say whether researchers will ever be able to turn the compounds, 2,3-butanedione and 1-hexanol, into an economical and environmentally benign insect repellent that works on mosquitoes generally.

But if they can, it would be a boon whose benefits might spread far beyond New Jersey, to the regions of the world where malaria is common, and where researchers and health workers argue about whether and how they can use DDT to combat it.

According to the World Health Organization, about 250 million people contract malaria each year, and about 900,000 of them die of it. Almost all of them are children.

Here’s a YouTube video that explains how the compounds work:

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.